The present disclosure relates generally to pressure/flow control systems and methods for treating a medical condition. In some instances, embodiments of the present disclosure are configured to be part of an IOP control system for the treatment of ophthalmic conditions.
Glaucoma, a group of eye diseases affecting the retina and optic nerve, is one of the leading causes of blindness worldwide. Most forms of glaucoma result when the intraocular pressure (IOP) increases to pressures above normal for prolonged periods of time. IOP can increase due to high resistance to the drainage of the fluid relative to its production. Left untreated, an elevated IOP causes irreversible damage to the optic nerve and retinal fibers resulting in a progressive, permanent loss of vision.
FIG. 1 is a diagram of the front portion of an eye 10 that helps to explain the processes of glaucoma. FIG. 1 shows a representation of the lens 12, cornea 14, iris 16, ciliary body 18, pars plana 20, pars plicata 22, trabecular meshwork 24, Schlemm's canal 26, anterior chamber 28, posterior chamber 30, sclera 32, retina 34, choroid 36, limbus 38, suspensory ligaments or zonules 40, suprachoroidal space 42, conjunctiva 44, and posterior segment 50.
The ciliary body 18 forms an annular ring around and posterior to the lens 12 and lies beneath the iris 16 and adjacent to the lens 12. The ciliary body 18 includes the pars plana 20 and pars plicata 22. The pars plicata 22 contains finger-like projections called ciliary processes and is the anterior portion of the ring that is the ciliary body 18 The pars plana 20 is the posterior portion of this ring. The ciliary body 18 continuously produces clear fluid that fills the anterior segment of the eye 10 (the space between the cornea 14 and lens 12). The fluid washes over the lens 12 and iris 16 and flows out of the anterior chamber 28 (the space between the cornea 14 and iris 16) through the canalicular and the uveoscleral pathways, both of which contribute to the fluid drainage system. The delicate balance between the production and drainage of fluid determines the IOP of the eye 10.
After production by the ciliary body 18, the fluid may leave the eye 10 by several different routes. Some fluid goes posteriorly through the vitreous body behind the lens 12 to the retina 34, while most circulates in the anterior segment of the eye to nourish avascular structures such as the lens 12 and the cornea 14 before outflowing by two major routes: the conventional outflow path 46 and the uveoscleral outflow path 48.
The angle of the anterior chamber 28, which extends circumferentially around the iris 16, contains structures that allow the fluid to drain. The conventional outflow path (or trabecular) route is the main mechanism of outflow, accounting for a large percentage of fluid egress. This route extends from the anterior chamber angle (formed by the iris 16 and the cornea 14), through the trabecular meshwork 24, into Schlemm's canal 26. The trabecular meshwork 24, which extends circumferentially around the anterior chamber 28, is commonly implicated in glaucoma. The trabecular meshwork 24 may act as a filter, limiting the outflow of fluid and providing a back pressure that directly relates to IOP. Schlemm's canal 26 is located just peripheral to the trabecular meshwork 24. Schlemm's canal 26 is fluidically coupled to collector channels (not shown) allowing fluid to flow out of the anterior chamber 28. The arrows 46 show the flow of fluid from the ciliary body 18, over the lens 12, over the iris 16, through the trabecular meshwork 24, and into Schlemm's canal 26 and its collector channels (to eventually reunite with the bloodstream in the episcleral vessels (not shown).
The uveoscleral outflow path 48 accounts for the major remainder of fluid egress in a normal eye 10, and also begins in the anterior chamber angle. Though the anatomy of the uveoscleral route 48 is less clear, fluid is likely absorbed by portions of the peripheral iris 16, and the ciliary body 18, after which it passes into the suprachoroidal space 42. As shown in FIG. 2a, the suprachoroidal space 42 is a potential space of loose connective tissue between the sclera 32 and the choroid 36 that provides a pathway for uveoscleral outflow. Normally the suprachoroidal space 42 is not evident due to the close apposition of the choroid 36 to the sclera 32 from the intraocular pressure of the eye 10. As shown in FIG. 2b, however, the tissues separate to form the suprachoroidal space 42 when fluid accumulates between the tissues. Fluid exits the eye 10 along the length of the suprachoroidal space 42 to eventually reunite with the bloodstream in the episcleral vessels.
One method of treating glaucoma includes implanting a drainage device in a patient's eye. These drainage devices works by bypassing the eye's own trabecular meshwork 24 and instead create an outflow of fluid through a small tube into a drainage site that may be a chamber in the eye 10, space between tissue in and around the eye 10, or a bleb. The drainage device allows fluid to flow from the interior chambers of the eye 10 to a drainage site, relieving pressure in the eye 10 and thus lowering IOP. Drainage devices that drain into the subconjunctival space require that a functional subconjunctival bleb be maintained to allow fluid to be absorbed and drained away. However, subconjunctival blebs are associated with several complications, including bleb failure due to fibrosis, conjunctival leakage, infections, and/or endophthalmitis.
One type of drainage device is the so-called “ab externo, plate style” glaucoma implant. In these ab externo, plate style devices, a flow or drainage tube is inserted into the anterior chamber of the eye 10 from outside the eye 10. A small plate is implanted underneath the conjunctiva 44 to allow flow of fluid out of the eye 10 into the subconjunctival space. These ab externo, plate style devices may require considerable manipulation of the conjunctiva 44 or other drainage site during implantation. Manipulation of these ocular tissues may lead to increased scarring at the delivery site (e.g., the conjunctival bleb), thereby increasing the rate of failure of the drainage device.
Further, inserting drainage devices into the anterior chamber 28 creates the risk of trauma to the cornea 14 or iris 16, which can lead to various adverse events or complications. In addition, tissue within the anterior chamber 28 may occlude the inlet to the drainage device, which can lead to failure of the device.
The system and methods disclosed herein overcome one or more of the deficiencies of the prior art.